.\" $OpenBSD: EVP_DigestInit.3,v 1.35 2024/08/30 07:03:19 tb Exp $
.\" full merge up to: OpenSSL 7f572e95 Dec 2 13:57:04 2015 +0000
.\" selective merge up to: OpenSSL 24a535ea Sep 22 13:14:20 2020 +0100
.\"
.\" This file is a derived work.
.\" The changes are covered by the following Copyright and license:
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.\" Copyright (c) 2019, 2023 Ingo Schwarze <schwarze@openbsd.org>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
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.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.\" The original file was written by Dr. Stephen Henson <steve@openssl.org>,
.\" Richard Levitte <levitte@openssl.org>,
.\" Paul Yang <yang.yang@baishancloud.com>, and
.\" Antoine Salon <asalon@vmware.com>.
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.Dd $Mdocdate: August 30 2024 $
.Dt EVP_DIGESTINIT 3
.Os
.Sh NAME
.Nm EVP_MD_CTX_new ,
.Nm EVP_MD_CTX_reset ,
.Nm EVP_MD_CTX_free ,
.Nm EVP_MD_CTX_init ,
.Nm EVP_MD_CTX_create ,
.Nm EVP_MD_CTX_cleanup ,
.Nm EVP_MD_CTX_destroy ,
.Nm EVP_DigestInit_ex ,
.Nm EVP_DigestUpdate ,
.Nm EVP_DigestFinal_ex ,
.Nm EVP_Digest ,
.Nm EVP_MD_CTX_copy_ex ,
.Nm EVP_DigestInit ,
.Nm EVP_DigestFinal ,
.Nm EVP_MD_CTX_copy ,
.Nm EVP_MD_CTX_md ,
.Nm EVP_md_null ,
.Nm EVP_sha224 ,
.Nm EVP_sha256 ,
.Nm EVP_sha384 ,
.Nm EVP_sha512 ,
.Nm EVP_sha512_224 ,
.Nm EVP_sha512_256 ,
.Nm EVP_ripemd160 ,
.Nm EVP_get_digestbyname ,
.Nm EVP_get_digestbynid ,
.Nm EVP_get_digestbyobj
.Nd EVP digest routines
.Sh SYNOPSIS
.In openssl/evp.h
.Ft EVP_MD_CTX *
.Fn EVP_MD_CTX_new void
.Ft int
.Fo EVP_MD_CTX_reset
.Fa "EVP_MD_CTX *ctx"
.Fc
.Ft void
.Fo EVP_MD_CTX_free
.Fa "EVP_MD_CTX *ctx"
.Fc
.Ft void
.Fo EVP_MD_CTX_init
.Fa "EVP_MD_CTX *ctx"
.Fc
.Ft EVP_MD_CTX *
.Fn EVP_MD_CTX_create void
.Ft int
.Fo EVP_MD_CTX_cleanup
.Fa "EVP_MD_CTX *ctx"
.Fc
.Ft void
.Fo EVP_MD_CTX_destroy
.Fa "EVP_MD_CTX *ctx"
.Fc
.Ft int
.Fo EVP_DigestInit_ex
.Fa "EVP_MD_CTX *ctx"
.Fa "const EVP_MD *type"
.Fa "ENGINE *engine"
.Fc
.Ft int
.Fo EVP_DigestUpdate
.Fa "EVP_MD_CTX *ctx"
.Fa "const void *d"
.Fa "size_t cnt"
.Fc
.Ft int
.Fo EVP_DigestFinal_ex
.Fa "EVP_MD_CTX *ctx"
.Fa "unsigned char *md"
.Fa "unsigned int *s"
.Fc
.Ft int
.Fo EVP_Digest
.Fa "const void *d"
.Fa "size_t cnt"
.Fa "unsigned char *md"
.Fa "unsigned int *s"
.Fa "const EVP_MD *type"
.Fa "ENGINE *engine"
.Fc
.Ft int
.Fo EVP_MD_CTX_copy_ex
.Fa "EVP_MD_CTX *out"
.Fa "const EVP_MD_CTX *in"
.Fc
.Ft int
.Fo EVP_DigestInit
.Fa "EVP_MD_CTX *ctx"
.Fa "const EVP_MD *type"
.Fc
.Ft int
.Fo EVP_DigestFinal
.Fa "EVP_MD_CTX *ctx"
.Fa "unsigned char *md"
.Fa "unsigned int *s"
.Fc
.Ft int
.Fo EVP_MD_CTX_copy
.Fa "EVP_MD_CTX *out"
.Fa "EVP_MD_CTX *in"
.Fc
.Ft const EVP_MD *
.Fo EVP_MD_CTX_md
.Fa "const EVP_MD_CTX *ctx"
.Fc
.Ft const EVP_MD *
.Fn EVP_md_null void
.Ft const EVP_MD *
.Fn EVP_sha224 void
.Ft const EVP_MD *
.Fn EVP_sha256 void
.Ft const EVP_MD *
.Fn EVP_sha384 void
.Ft const EVP_MD *
.Fn EVP_sha512 void
.Ft const EVP_MD *
.Fn EVP_sha512_224 void
.Ft const EVP_MD *
.Fn EVP_sha512_256 void
.Ft const EVP_MD *
.Fn EVP_ripemd160 void
.Ft const EVP_MD *
.Fo EVP_get_digestbyname
.Fa "const char *name"
.Fc
.Ft const EVP_MD *
.Fo EVP_get_digestbynid
.Fa "int type"
.Fc
.Ft const EVP_MD *
.Fo EVP_get_digestbyobj
.Fa "const ASN1_OBJECT *o"
.Fc
.Sh DESCRIPTION
The EVP digest routines are a high-level interface to message digests
and should be used instead of the cipher-specific functions.
.Pp
.Fn EVP_MD_CTX_new
allocates a new, empty digest context.
.Pp
.Fn EVP_MD_CTX_reset
cleans up
.Fa ctx
and resets it to the state it had after
.Fn EVP_MD_CTX_new ,
such that it can be reused.
.Pp
.Fn EVP_MD_CTX_free
cleans up
.Fa ctx
and frees the space allocated to it.
.Pp
.Fn EVP_MD_CTX_init
is a deprecated function to clear a digest context on the stack
before use.
Do not use it on a digest context returned from
.Fn EVP_MD_CTX_new
or one that was already used.
.Pp
.Fn EVP_MD_CTX_create ,
.Fn EVP_MD_CTX_cleanup ,
and
.Fn EVP_MD_CTX_destroy
are deprecated aliases for
.Fn EVP_MD_CTX_new ,
.Fn EVP_MD_CTX_reset ,
and
.Fn EVP_MD_CTX_free ,
respectively.
.Pp
.Fn EVP_DigestInit_ex
sets up the digest context
.Fa ctx
to use a digest
.Fa type .
The
.Fa type
will typically be supplied by a function such as
.Fn EVP_sha512 .
The
.Fa ENGINE *engine
argument is always ignored and passing
.Dv NULL
is recommended.
.Pp
.Fn EVP_DigestUpdate
hashes
.Fa cnt
bytes of data at
.Fa d
into the digest context
.Fa ctx .
This function can be called several times on the same
.Fa ctx
to hash additional data.
.Pp
.Fn EVP_DigestFinal_ex
retrieves the digest value from
.Fa ctx
and places it in
.Fa md .
If the
.Fa s
parameter is not
.Dv NULL ,
then the number of bytes of data written (i.e. the length of the
digest) will be written to the integer at
.Fa s ;
at most
.Dv EVP_MAX_MD_SIZE
bytes will be written.
After calling
.Fn EVP_DigestFinal_ex ,
no additional calls to
.Fn EVP_DigestUpdate
can be made, but
.Fn EVP_DigestInit_ex
can be called to initialize a new digest operation.
.Pp
.Fn EVP_Digest
is a simple wrapper function to hash
.Fa cnt
bytes of data at
.Fa d
using the digest
.Fa type
in a one-shot operation and place the digest value into
.Fa md ,
and, unless
.Fa s
is
.Dv NULL ,
the length of the digest in bytes into
.Pf * Fa s .
This wrapper uses a temporary digest context and passes its arguments to
.Fn EVP_DigestInit_ex ,
.Fn EVP_DigestUpdate ,
and
.Fn EVP_DigestFinal_ex
internally.
The
.Fa ENGINE *engine
argument is always ignored and passing
.Dv NULL
is recommended.
.Pp
.Fn EVP_MD_CTX_copy_ex
can be used to copy the message digest state from
.Fa in
to
.Fa out .
This is useful if large amounts of data are to be hashed which only
differ in the last few bytes.
.Pp
.Fn EVP_DigestInit
is a deprecated function behaving like
.Fn EVP_DigestInit_ex
except that it requires
.Fn EVP_MD_CTX_reset
before it can be used on a context that was already used.
.Pp
.Fn EVP_DigestFinal
is a deprecated function behaving like
.Fn EVP_DigestFinal_ex
except that the digest context
.Fa ctx
is automatically cleaned up after use by calling
.Fn EVP_MD_CTX_reset
internally.
.Pp
.Fn EVP_MD_CTX_copy
is a deprecated function behaving like
.Fn EVP_MD_CTX_copy_ex
except that it requires
.Fn EVP_MD_CTX_reset
before a context that was already used can be passed as
.Fa out .
.Pp
.Fn EVP_sha224 ,
.Fn EVP_sha256 ,
.Fn EVP_sha384 ,
.Fn EVP_sha512 ,
and
.Fn EVP_ripemd160
return
.Vt EVP_MD
structures for the SHA224, SHA256, SHA384, SHA512 and
RIPEMD160 digest algorithms respectively.
.Pp
.Fn EVP_sha512_224
and
.Fn EVP_sha512_256
return an
.Vt EVP_MD
structure that provides the truncated SHA512 variants SHA512/224 and SHA512/256,
respectively.
.Pp
.Fn EVP_md_null
is a "null" message digest that does nothing:
i.e. the hash it returns is of zero length.
.Pp
.Fn EVP_get_digestbyname ,
.Fn EVP_get_digestbynid ,
and
.Fn EVP_get_digestbyobj
return an
.Vt EVP_MD
structure when passed a digest name, a digest NID, or an ASN1_OBJECT
structure respectively.
.Pp
.Fn EVP_get_digestbynid
and
.Fn EVP_get_digestbyobj
are implemented as macros.
.Pp
The EVP interface to message digests should almost always be used
in preference to the low-level interfaces.
This is because the code then becomes transparent to the digest used and
much more flexible.
.Pp
The
.Fa ENGINE *engine
argument is always ignored and passing
.Dv NULL
is recommended.
.Pp
The functions
.Fn EVP_DigestInit ,
.Fn EVP_DigestFinal ,
and
.Fn EVP_MD_CTX_copy
are obsolete but are retained to maintain compatibility with existing
code.
New applications should use
.Fn EVP_DigestInit_ex ,
.Fn EVP_DigestFinal_ex ,
and
.Fn EVP_MD_CTX_copy_ex
because they can efficiently reuse a digest context instead of
initializing and cleaning it up on each call.
.Pp
If digest contexts are not cleaned up after use, memory leaks will occur.
.Sh RETURN VALUES
.Fn EVP_MD_CTX_new
and
.Fn EVP_MD_CTX_create
return the new
.Vt EVP_MD_CTX
object or
.Dv NULL
for failure.
.Pp
.Fn EVP_MD_CTX_reset
and
.Fn EVP_MD_CTX_cleanup
always return 1.
.Pp
.Fn EVP_DigestInit_ex ,
.Fn EVP_DigestUpdate ,
.Fn EVP_DigestFinal_ex ,
.Fn EVP_Digest ,
.Fn EVP_MD_CTX_copy_ex ,
.Fn EVP_DigestInit ,
.Fn EVP_DigestFinal ,
and
.Fn EVP_MD_CTX_copy
return 1 for success or 0 for failure.
.Pp
.Fn EVP_MD_CTX_md
returns the
.Vt EVP_MD
object used by
.Fa ctx ,
or
.Dv NULL
if
.Fa ctx
is
.Dv NULL
or does not have any message digest algorithm assigned yet.
.Pp
.Fn EVP_md_null ,
.Fn EVP_sha224 ,
.Fn EVP_sha256 ,
.Fn EVP_sha384 ,
.Fn EVP_sha512 ,
.Fn EVP_sha512_224 ,
.Fn EVP_sha512_256 ,
and
.Fn EVP_ripemd160
return pointers to constant static objects owned by the library.
.Pp
.Fn EVP_get_digestbyname ,
.Fn EVP_get_digestbynid ,
and
.Fn EVP_get_digestbyobj
return either an
.Vt EVP_MD
structure or
.Dv NULL
if an error occurs.
.Sh EXAMPLES
This example digests the data "Test Message\en" and "Hello World\en",
using the digest name passed on the command line.
.Bd -literal -offset indent
#include <stdio.h>
#include <string.h>
#include <openssl/evp.h>

int
main(int argc, char *argv[])
{
	EVP_MD_CTX *mdctx;
	const EVP_MD *md;
	const char mess1[] = "Test Message\en";
	const char mess2[] = "Hello World\en";
	unsigned char md_value[EVP_MAX_MD_SIZE];
	unsigned int md_len, i;

	if (argc <= 1) {
		printf("Usage: mdtest digestname\en");
		exit(1);
	}

	md = EVP_get_digestbyname(argv[1]);
	if (md == NULL) {
		printf("Unknown message digest %s\en", argv[1]);
		exit(1);
	}

	mdctx = EVP_MD_CTX_new();
	EVP_DigestInit_ex(mdctx, md, NULL);
	EVP_DigestUpdate(mdctx, mess1, strlen(mess1));
	EVP_DigestUpdate(mdctx, mess2, strlen(mess2));
	EVP_DigestFinal_ex(mdctx, md_value, &md_len);
	EVP_MD_CTX_free(mdctx);

	printf("Digest is: ");
	for(i = 0; i < md_len; i++)
		printf("%02x", md_value[i]);
	printf("\en");

	return 0;
}
.Ed
.Sh SEE ALSO
.Xr BIO_f_md 3 ,
.Xr CMAC_Init 3 ,
.Xr evp 3 ,
.Xr EVP_BytesToKey 3 ,
.Xr EVP_DigestSignInit 3 ,
.Xr EVP_DigestVerifyInit 3 ,
.Xr EVP_MD_CTX_ctrl 3 ,
.Xr EVP_MD_nid 3 ,
.Xr EVP_PKEY_CTX_set_signature_md 3 ,
.Xr EVP_PKEY_meth_set_signctx 3 ,
.Xr EVP_sha1 3 ,
.Xr EVP_sha3_224 3 ,
.Xr EVP_SignInit 3 ,
.Xr EVP_sm3 3 ,
.Xr EVP_VerifyInit 3 ,
.Xr HMAC 3 ,
.Xr OCSP_basic_sign 3 ,
.Xr OCSP_request_sign 3 ,
.Xr PKCS5_PBKDF2_HMAC 3 ,
.Xr PKCS7_sign_add_signer 3 ,
.Xr X509_ALGOR_set0 3 ,
.Xr X509_digest 3 ,
.Xr X509_sign 3
.Sh HISTORY
.Fn EVP_DigestInit ,
.Fn EVP_DigestUpdate ,
and
.Fn EVP_DigestFinal
first appeared in SSLeay 0.5.1.
.Fn EVP_md_null
and
.Fn EVP_get_digestbyname
first appeared in SSLeay 0.8.0.
.Fn EVP_get_digestbynid
and
.Fn EVP_get_digestbyobj
first appeared in SSLeay 0.8.1.
.Fn EVP_ripemd160
first appeared in SSLeay 0.9.0.
All these functions have been available since
.Ox 2.4 .
.Pp
.Fn EVP_MD_CTX_copy
first appeared in OpenSSL 0.9.2b and has been available since
.Ox 2.6 .
.Pp
.Fn EVP_MD_CTX_md
first appeared in OpenSSL 0.9.5 and has been available since
.Ox 2.7 .
.Pp
.Fn EVP_MD_CTX_init ,
.Fn EVP_MD_CTX_create ,
.Fn EVP_MD_CTX_cleanup ,
.Fn EVP_MD_CTX_destroy ,
.Fn EVP_DigestInit_ex ,
.Fn EVP_DigestFinal_ex ,
.Fn EVP_Digest ,
and
.Fn EVP_MD_CTX_copy_ex
first appeared in OpenSSL 0.9.7 and have been available since
.Ox 3.2 .
.Pp
.Fn EVP_sha224 ,
.Fn EVP_sha256 ,
.Fn EVP_sha384 ,
and
.Fn EVP_sha512
first appeared in OpenSSL 0.9.7h and 0.9.8a
and have been available since
.Ox 4.0 .
.Pp
.Fn EVP_MD_CTX_new ,
.Fn EVP_MD_CTX_reset ,
and
.Fn EVP_MD_CTX_free
first appeared in OpenSSL 1.1.0 and have been available since
.Ox 6.3 .
.Pp
.Fn EVP_sha512_224
and
.Fn EVP_sha512_256
first appeared in OpenSSL 1.1.1 and have been available since
.Ox 7.4 .
